Downloads, Play files and Linux files can be modified from the files list, including cut, rename and delete (except for Play files).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/58920656be2e03e2a64e6cbb4080c10d5159f4ba

commit 58920656be2e03e2a64e6cbb4080c10d5159f4ba
Author: Sam McNally <sammc@chromium.org>
Date: Fri Jan 11 06:26:57 2019

Remove inappropriate context menu items for roots within My files.

Users should not be able to copy, rename, delete etc. roots (Play Files
and Linux Files) and Downloads within My files.

However, due to CommandUtil.isRootEntry() failing to handle VolumeEntry
properly, and the lack of special-casing for Downloads, these actions
are allowed.

Change CommandUtil.isRootEntry() to use util.isSameEntry() so roots are
correctly identified. Special case My files/Downloads for
CommandUtil.shouldShowMenuItemsForEntry() to treat it as a root. Hide
copy, cut and zip selection (as well as the rename and delete) for any
entry where CommandUtil.shouldShowMenuItemsForEntry() returns false.

Bug:  916952 
Change-Id: I7f0eb716fc1b61e9edb2dd763b9bc2c672c0b982
Reviewed-on: https://chromium-review.googlesource.com/c/1405160
Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621925}
[modify] https://crrev.com/58920656be2e03e2a64e6cbb4080c10d5159f4ba/chrome/browser/chromeos/file_manager/file_manager_browsertest.cc
[modify] https://crrev.com/58920656be2e03e2a64e6cbb4080c10d5159f4ba/ui/file_manager/file_manager/foreground/js/file_manager_commands.js
[modify] https://crrev.com/58920656be2e03e2a64e6cbb4080c10d5159f4ba/ui/file_manager/file_manager/foreground/js/file_transfer_controller.js
[modify] https://crrev.com/58920656be2e03e2a64e6cbb4080c10d5159f4ba/ui/file_manager/integration_tests/file_manager/context_menu.js